Alarm system

ABSTRACT

An alarm system includes two separate electrical loop circuits and means, such as diodes, controlling the supply of electrical power to the circuits so that normally one of the circuits is energized during one part of a given time period, e.g. the positive half cycle of an alternating current source common to the two circuits, and the other of the circuits is energized during the other part of such time period, e.g. the negative half cycle of such alternating current source. Alarm-condition sensors and associated normally-open switch means provide interconnection between the two circuits in case of an alarm condition so that current flows in one of the circuits from the other during the time such one circuit is unenergized. Such one circuit has a bypass circuit portion containing alarm means and also has means for blocking normal current flow but not current flow from the other circuit, whereby the latter current flow activates the alarm means. Means may be provided in each circuit to indicate whether or not one of the other of the circuits becomes opened or shorted. A third circuit may be provided as a ground check.

United States Patent Winger May 14, 1974 ALARM SYSTEM PrimaryExaminer-Thomas B. Habecker 75 Inventor: William A. Winger, Salt LakeAmmey, FvmMallmckrodr &

County, Utah Mallinckrodt [73] Assignee: United States Smelling Refiningand Mining Company, New York, NY. ABSTRACT [22] i June 7 1972 An alarmsystem includes two separate electrical loop [52] US. Cl 340/409,340/176, 340/227 C [51] Int. Cl. G08b 17/00, G08b 29/00 5 8] Field ofSearch 340/409 [56] References Cited UNITED STATES PATENTS 3,010,100ll/l96l Muehtcr 340/409 3,103,652 9/1963 Thorshecm 340/409 3,521,2767/1970 Rabcr .I 340/409 3,587,095 6/1971 Earling 340/409- 3,588,8916/1971 Porter 340/409 3,603,949 9/1971 Walthard 340/409 1,537,211 5/1925Wootton 340/409 2,569,338 9/1951 Richmond 340/409 2,944,251 7/1960Tetherow 340/409 3,401,384 9/1968 Highstone.... 340/409 3,618,06911/1971 Evans 340/409 circuits and means, such as diodes, controllingthe supply of electrical power to the circuits so that normally one ofthe circuits is energized during one part of a given time period, eg thepositive half cycle of an alternating current source common to the twocircuits, and the other of the circuits is energized during the otherpart of such time period, e.g. the negative half cycle of suchalternating current source. Alarmcondition sensors and associatednormally-open switch means provide interconnection between the twocircuits in case of an alarm condition so that current flows in one ofthe circuits from the other during the time such one circuit isunenergized. Such one circuit has a by-pass circuit portion containingalarm means and also has means for blocking normal current flow but notcurrent flow from the other circuit, whereby the latter current flowactivates the alarm means. Means may be provided'in each circuit toindicate whether or not one of the other of the circuits becomes opcnedor shorted. A third circuit may be provided as a ground check.

13 Claims, 3 Drawing Figures PATENIEUMAYMIBM SHEET 1 BF 2 FIG. I

I CIRCUIT B RETURN CLOSED ALARM CONDITION SENSOR 09E A 9MT H ./F

FLOW HALARM CURRENT CONTROL 2ND TIME PERIOD CIRCUIT ENERGIZING MEANSPERIODICALLY VARYING POWER I ISTI TIME I I I I L I. A I A A FIG. 2

PATENTED MAY 1 4 I974 sum 2 0F 2 OBJECTIVE:

In the making of this invention it was a primary objective to provide analarm system, without redundant circuitry, which would be-reliable,relatively inexpensive, simple in construction and maintenance, andrelativelyfail-safe, so as to be particularly useful as an alarm systemin coal mines where strict government regulations now set high standardsof reliability and where very long conveyor systems extending throughunderground haulageways require extensive alarm installations if therequired protection is to be provided.

SUMMARY OF THE INVENTION In accordance with the invention, an alarmsystem has two separate electrical loop circuits and means forenergizing such circuits alternately. Alarm-conditionsensing means withassociated, normally open, switch means are provided to interconnect thecircuits when an alarm conditionoccurs, such interconnection allowingcurrent from the energized circuit to flow in the non-energized circuit;An alarm and associated current-flow-control means are provided in atleast one of the circuits, so current flowing from the other circuitinto such one circuit will actuate the alarm but normal current flow inthat one circuit will not. Indicating means are usually provided in eachcircuit to show that current either is or is not flowing normally,thereby warning of any system malfunction that interferes with normalcurrent flow.

It is preferred thatthe currentsupplied to the two electrical circuitsbe alternating, with the positive halfcycle going to one of the circuitsand the negative half- .cycle going to the other.

The system also may be provided with a ground loop for thealarm-condition-sensing means, such ground loop having indicating meansoperative if any ground short occurs within the system. Such ground loopis preferably separate from the other two circuits, as a third circuit,and may be provided with additional indicating means for showing whetheror not the ground circuit is itself broken.

THE DRAWINGS A specific embodiment presently contemplated as the bestmode of carrying out the invention is shown in the accompanying drawingsin which:

FIG. 1 is a simplified block diagram indicative of the inventiveconcepts;

- cycle, AC power from the usual power line source 13,.

FIG. 2, an abbreviated wiring diagram of a specific system correspondingto FIG. 1, with arrows showing the flow of current when an alarmcondition is sensed; and

FIG. 3, a detailed wiring diagram of the system of FIG. 2 shown indetail and including a ground loop, the system being designed for use ina coal mine in connection with conveyor systems extending over longdistances through underground haulageways.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT As indicated in FIG.1, the alarm system of the invention comprises two separate electricalcircuits of closed loop character designated A and B, respectively. Thetwo circuits are adapted to be electrically interconnected by a normallyopen switch associated with an alarm-condition sensor that acts to closethe switch upon the occurrence of an alarm condition. Any number ofswitches and associated sensors can be utilized, depending upon thenature and extent of the area to be protected. 4

Under normal conditions, circuit-energizing power that variesperiodically, e.g. positive and negative half cycles of AC, flowsthrough each circuit alternately.

When an alarm-condition, such as excessive heat, is sensed by thealarm-condition sensor and the switch thereof closes and interconnectsthe two circuits A and B, current flows from circuit A into circuit B.That circuit is provided with an alarm device, usually a relay connectedso as to activate an audio alarm such as a bell, and with associatedcurrent flow control means,

such as diodes, for blocking normal current flow but for passing theopposite current flow from circuit A. Thus,

when an alarm-condition is sensed, an alarm is given. Thesystemconstantly stands ready to give an alarm. In the specific instanceillustrated from an abbreviated standpoint in FIG. 2 and in full detailin FIG. 3, commercially available units 10 known as temperature risesensors are utilized at intervals along the length of a coal conveyorsystem in an underground haulageway of a coal mine to sense temperaturerise beyond a predetermined danger point and to actuate the alarm systemaccordingly. As shown, there are three of the units 10, but only one ormany more could be employed depending upon the need.

Each of the sensor units 10 includes a normally open switch 10a, withone switch terminal in circuit A and the other in circuit B. The switchis normally maintained open in conventional manner by suitableheatreleasable means (not shown), and an electrically con ductivecasing, indicated at 10b, FIG. 3, is electrically connected to a groundcheck circuit C.

Diodes D1 and D2 and a relay 11 are provided in circuit A, and diodes D3and D4 and a relay 12 in circuit The alarm system may be supplied with 110 volt, 60

FIG. 2, but is preferably designed to operate from a twelve volt DCstorage-type battery in case of AC power line failure.

' In the power supply illustrated in FIG. 3, uninterrupted AC power isprovided at all times. The l 10 volt AC line power is reduced to 13.9volt DC power by a standard AC to DC converter 14. Diodes D5, D6, and D7are provided to further reduce the DC voltage before it is applied tothe terminals of storage battery 15.

More or fewer diodes could be provided to adjust the voltage applied tothe storage battery to any desired level. The terminals of storagebattery 15 are also connected to a standard l2 volt DC to 1 volt ACinverter 16. The rectified reduced voltage power supplied to batteryfrom the line recharges the battery if it is in need of recharge andalso supplies the power to operate inverter 16. If the AC line shouldfail, the battery maintains the power to the inverter. Thus, nointerruption is caused in inverter output. The l 10 volt AC output ofthe inverter is supplied directly to circuits A and B through electricallines 17 and 18 and the normally closed relay contacts 19a and 19b ofrelay 19.

Diodes D1 and D2 are arranged to allow current to flow in circuit A whenthe voltage at 19a is positive with respect to 19b, i.e., during thepositive half-cycle of the AC power, while diodes D3 and D4 are arrangedto block current flow into and through circuit B during this time. Whenthe voltage at 19a becomes negative with respect to' 19b, i.e., duringthe negative half-cycle of the AC power, diodes D1 and D2 in circuit Ablock current flow while diodes D3 and D4 in circuit B allow current toflow into and through that circuit. Thus, circuit A will be energizedduring each positive half-cycle and circuit B during each negativehalf-cycle, resulting in each circuit being alternately energized 60times each second.

Relay 11 in circuit A constitutes the control portion of indicator meansthat indicates proper current flow within the circuit. When currentflows in circuit A, it energizes the coil of relay 11. Since a relaycoil acts as an inductor, it will oppose any change in current flowtherethrough. Thus, as the current stops flowing in circuit A, the coilof relay 11 produces a voltage pulse of similar polarity, which will bepassed by a diode D8 in shunt circuit 20. This voltage pulse willmaintain the relay in energized position for a fraction of a secondafter circuit A is de-energized. The time that relay 11 remainsenergized is longer than H] 20th ofa second in this case, and, since thecircuit is de-energized for only half a cycle on each cycle, i.e., forl/l20th ofa second, the circuit is re-energized before the relay isdeenergized. Relay 11 thus remains in energized position as long ascircuit A is functioning properly, with the normally closed relaycontacts 11a positively held open. Such contacts are connected incircuit with a signal light 21, so as to keep such light turned off whenrelay 11 is energized and circuit A is operating normally. When relay 11becomes de-energized, by reason of a lack of current flow in circuit A,contacts 11a assume their normally closed positions, and signal light 21is turned on, thereby indicating that there is a malfunction in circuitA. It should be realized that various other arrangements are possible toprovide the desired indication of circuit malfunction.

Relay 12 in circuit B, normally closed relay contacts 120, diode D10 inshunt circuit 22, and signal light 24 operate in similar manner to warnof a malfunction causing lack of current flow in circuit B.

In case of fire or other rise in temperature beyond the preset maximum,one or more of the temperature-rise sensors 10 will have its switch 10aclosed, thereby interconnecting circuits A and B. During the positivehalf cycle, when circuit A is energized, current will flow from circuitA through the closed switch or switches 10a into circuit B, throughdiode D11, relay 25, and

diode D12. Relay 25, which under normal conditions is prevented frombeing energized by blocking diodes D11 and D12, is energized in responseto the current from circuit A flowing through circuit B. Relay 25 and adiode D13 in shunt circuit 26'now act similarly to relays 11 and 12 andtheir associate diodes D8 and D10, respectively, and remain energized,even though energizing current from circuit A occurs only during eachpositive half cycle. In the present case, normally-open relay contacts25a close and cause energization of permanent-magnet-type self-lockingrelay 19, which, in turn, causes normally-closed relay contacts 19a and19b to open, shutting off power to both circuits A and B and causingnormally-open relay contacts to close, thereby activating a bell 27 andflashing red lights 28. The energizing current for relay 19 comesdirectly from the AC output of the inverter 16 and is rectified by diodeD14. This energizing current is only momentary, because of the openingof relay contacts 19 e. Once energized, however, the relay remains inenergized position because of a small permanent magnet within the relay.The self-locking of relay 19 is required because power is disconnectedfrom circuits A and B as previously indicated, causing alarm relay 25 tobecome de-energized.- Because it is desired to continue operation of thealarm devices and not to restore power to the circuits A and B until theproper personnel are alerted and the alarm condition corrected, thealarm devices are turned off and power restored to such cir cuits onlyby momentarily closing reset switch S1, thereby causing current to flowthrough the relay contacts 19d, resistor R1, diode D15, and the coil ofrelay 19. Diode D15 is arranged electrically opposite to diode D14, sothat the rectified reset current passing through relay 19 is of oppositepolarity to the energizing current. The magnetic field thus createdopposes that of the permanent magnet and causes the relay to return toits de-energized position; Resistor R1 limits current flow. If the alarmcondition has not been corrected in the meantime, relay 19 willimmediately become re-energized due to re-energization of alarm relay25. Relay 25 and relay 19 may be also utilized to shut off power tooperating equipment, turn on fire sprinkler systems, etc.

The same results are obtained if, for some reason, the two circuits Aand B become shorted. Thus, an'effective fire sensing system can beprovided if, instead of the temperature rise sensors 10, wires havinginsulation designed to melt at a predetermined temperature and arranged'so that upon melting of the insulation the wires come into electricalcontact and cause an electricalshort circuit, are utilized.

Relay 25 and its associated diodes could be placed in circuit A ratherthan circuit B, so as to be activated by the current from circuit Bflowing through circuit A upon interconnection of the two circuits.Also, a similar relay and its associated diodes could be included ineach of the circuits A and B, so that both would be energized uponinterconnection of the two circuits.

' A third or ground check circuit C, FIG. 3, is advantageously providedto indicate any grounding of the circuits A and B. In the formillustrated, circuit C comprises diodes D16 and D17 and relays 30 and31. Connections with ground are made between diodes D16 and D17 for allpoints of ground in the temperature rise sensors '10.

If circuit A should become grounded when energized during the positivehalf cycle, current would flow into ground circuit C and through diodeD17 to energize relay 31, which, as associated with diode D18, wouldremain energized in the manner previously explained. Normally-open relaycontacts 31a would close, causing light 32 to go on as a visualindication of the grounded conditionof circuit A. If circuit B shouldbecome grounded when energized during the negative I half cycle, currentwould flow into ground circuit C and through diode D16 to energize relay30, which, as associated with diode D19, would also remain energized aspreviously explained. Normally-open relay contacts 30a would close,causing light 33 to go on as a visual indication of the groundedcondition of circuit B.

In order to continuously check ground circuit C for continuity and toprovide a warning if it is broken for any reason, an interconnectionbetween each of the two circuits A and B and the third circuit C is madeby means of neon lamps 34 and 35. During the positive half cycle,current flows from circuit A through neon lamp 34 into circuit C andthrough diode D17 and relay 31, thus lighting such lamp 34. The currentflowing through such neon lamp 34 is smaller than the current necessaryto energize relay 31, so that, even though the current flows throughrelay 31, it does not activate it. The voltage pulse produced by therelay during the other circuit upon interconnection of the twocircuitsin response to an alarm condition. Additionally, if desired, thesystem may be arranged for constant monitoring of both circuits by theprovision of means, e.g. a DC power supply connected to each circuit,for supplying electrical power continuously to both circuits asbackground power for energizing the indicating means, i.e.,loop-integrity monitors, in the respective circuits. If so arranged,suitable isolating means, such as capacitors and inductors appropriatelyinterposed between such DC power supplyand the AC power supply and inthe means adapted to interconnect the two circuits, should be provided.Moreover, the normal energization of the two circuits alternately, canbe replaced by pulse energization of the one circuit not containing thealarm means.

Whereas this invention is here illustrated with respect to a preferredspecific embodiment thereof, it should negative half cycle not onlymaintains the aforementioned small current flow through the relay, inconjunction with diode D18 as previously explained, but also maintainsjust enough current flow through neon lamp 35 to keep it lighted. Thepath from ground circuit C through neon lamp 35, diode D11, relay 25,and diode D12 is not followed by the current, because the voltage dropnecessary to initiate current flow along this path is large compared tothat necessary to initiate flow along the path through diode D17 andrelay 31, which is the path taken by the current.

If a break occurs in ground circuit C, current can no longer flow andneon lamp 34 will go out as a visual indication of that condition. Inorder to keep operative that portion of the alarm system which indicateselectrical grounds within the system, even though a break in groundcircuit C has occurred, a manual switch S2 provided for that purpose isclosed. This will cause neon lamp 34 to again light and circuit C willfunction as before described, to indicate electrical grounds. The causeof the ground-circuit-break indication should be located and correctedand switch S2 then opened.

During the negative half ,cycle, current flows from circuit B throughneon lamp 35, diode D16, and relay in a manner similar to that describedfor the positive half-cycle and will cause such lamp to light.Similarly, if a break occurs in ground circuit C, lamp 35 will go out.

A relay 36 is desirably provided to indicate whether the system isoperating on line voltage or from battery 15. A diode D20 rectifies theline AC power applied to relay 36, and such relay; as associated with adiode D21, will remain energized in the manner previously described solong as there is line AC power. Normallyopen relay contacts 36a areclosed and a light 37 is energized to indicate that line voltage ispresent. If line voltage is interrupted for any reason, relay 36 isdeenergized and normally-closed contacts 36b are closed, therebyenergizing a light 38, which indicates that the system is operating frombattery 15.

While a fire alarm system has been described, devices adapted to senseother dangerous conditions can be be realized that various changes maybe made therein and other specific forms may be constructed by thoseskilled in the art without departing from the invention concepts heredisclosed.

I claim:

1. An alarm system, including two separate electrical loop circuits;means for imposing currenton said circuits alternately; means forinterconnecting said circuits in response to an alarm condition; alarmmeans comprising an alarm current sensing means in one of said circuits;means for coupling said alarm sensing means into its circuit, saidcoupling means blocking normal current flow in that circuit and passingalarm current flow from the other circuit.

2. An alarm system according to claim 1, wherein the means forinterconnecting said circuitsin response to an alarm condition comprisesat least one temperaturerise sensor and normally open switch meansarranged to be closed by said sensor upon the sensing of an alarmcondition.

3. An alarm system according to claim 1, wherein the means for blockingnormal current flow in the alarm circuit and for passing alarm currentflow from the other circuit is a rectifier.

4. An alarm system according to claim 1, wherein the means for imposingcurrent on said circuits alternately comprises a source of AC power, andpower-blocking means operative to supply power to one circuit during thepositive half cycle of power and to the other circuit during thenegative half cycle of power.

5. An alarm system according to claim 4, wherein the power-blockingmeans comprises at least one'rectifying means in each of the twocircuits, the rectifying means in one circuit being of oppositeorientation to the rectifying means in the other circuit.

6. An alarm system according to claim 1, additionally includingindicating means in both circuits, said indicating means beingresponsive to normal current flow within the respectivecircuits. A

7. An alarm system according to claim 6, wherein each indicating meanscomprises signal means and a control relay therefor.

8. An alarm system according to claim 1, additionally including a groundcircuit; means interconnecting said ground circuit with both of theother circuits; and

means for indicating current flow between said other circuits and saidground circuit.

9. An alarm system according to claim 8, wherein both the meansinterconnecting the ground circuit with the other circuits and the meansfor indicating current flow between said other circuits and said thirdcircuit are electric lamps.

10. An alarm system according to claim 1, wherein the alarm meansincludes means in the alarm device circuit for controlling the operationof equipment in an alarm-protected areal 11. An alarm system accordingto claim 1, wherein the alarm means includes means in the alarm devicecircuit for de-activating the means for supplying power to the twocircuits.-

12. An alarm system according to claim 1, wherein the means forinterconnecting the two circuits in response to an alarm condition arewires provided with insulation which melts at a predeterminedtemperature, said wires being arranged to come into electrical contactwith each other and to establish a short in the system upon melting ofsaid insulation.

13. An alarm system, including two independent loop circuits havingrespective loop-integrity monitors; sensing means operative tointerconnect portions of said circuits in response to the occurrence ofan abnormal condition; abnormal-condition-evidencing means in at leastone of said circuits and responsive to the interconnection of saidportions of said loop circuits; an alternating-current power source; andfirst and second unidirectionally conducting means connecting saidsource to said two loop circuits for energizing the latter, said firstand second means being polarized to effect energization of said loopcircuits during alternate half-cycles of said power source, saidabnormal-conditionevidencing means being connected in one of said loopcircuits and having polarizing means causing operation thereof uponoccurrence of an abnormal condition selectively during the half-cyclesof condition of said first unidirectionally conducting means and notduring the half-cycles of conduction of said second unidirectionallyconducting means,

1. An alarm system, including two separate electrical loop circuits;means for imposing current on said circuits alternately; means forinterconnecting said circuits in response to an alarm condition; alarmmeans comprising an alarm current sensing means in one of said circuits;means for coupling said alarm sensing means into its circuit, saidcoupling means blocking normal current flow in that circuit and passingalarm current flow from the other circuit.
 2. An alarm system accordingto claim 1, wherein the means for interconnecting said circuits inresponse to an alarm condition comprises at least one temperature-risesensor and normally open switch means arranged to be closed by saidsensor upon the sensing of an alarm condition.
 3. An alarm systemaccording to claim 1, wherein the means for blocking normal current flowin the alarm circuit and for passing alarm current flow from the othercircuit is a rectifier.
 4. An alarm system according to claim 1, whereinthe means for imposing current on said circuits alternately comprises asource of AC power, and power-blocking means operative to supply powerto one circuit during the positive half cycle of power and to the othercircuit during the negative half cycle of power.
 5. An alarm systemaccording to claim 4, wherein the power-blocking means comprises atleast one rectifying means in each of the two circuits, the rectifyingmeans in one circuit being of opposite orientation to the rectifyingmeans in the other circuit.
 6. An alarm system according to claim 1,additionally including indicating means in both circuits, saidindicating means being responsive to normal current flow within therespective circuits.
 7. An alarm system according to claim 6, whereineach indicating means comprises signal means and a control relaytherefor.
 8. An alarm system according to claim 1, additionallyincluding a ground circuit; means interconnecting said ground circuitwith both of the other circuits; and means for indicating current flowbetween said other circuits and said ground circuit.
 9. An alarm systemaccording to claim 8, wherein both the means interconnecting the groundcircuit with the other circuits and the means for indicating currentflow between said other circuits and said third circuit are electriclamps.
 10. An alarm system according to claim 1, wherein the alarm meansincludes means in the alarm device circuit for controlling the operationof equipment in an alarm-protected area.
 11. An alarm system accordingto claim 1, wherein the alarm means includes means in the alarm devicecircuit for de-activating the means for supplying power to the twocircuits.
 12. An alarm system according to claim 1, wherein the meansfor interconnecting the two circuits in response to an alarm conditionare wires provided with insulation which melts at a predeterminedtemperature, said wires being arranged to come into electrical contactwith each other and to establish a short in the system upon melting ofsaid insulation.
 13. An alarm system, including two independent loopcircuits having respective loop-integrity monitors; sensing meansoperative to interconnect portions of said circuits in response to theoccurrence of an abnormal condition; abnormal-condition-evidencing meansin at least one of said circuits and responsive to the interconnectionof said portions of said loop circuits; an alternating-current powersource; and first and seconD unidirectionally conducting meansconnecting said source to said two loop circuits for energizing thelatter, said first and second means being polarized to effectenergization of said loop circuits during alternate half-cycles of saidpower source, said abnormal-condition-evidencing means being connectedin one of said loop circuits and having polarizing means causingoperation thereof upon occurrence of an abnormal condition selectivelyduring the half-cycles of condition of said first unidirectionallyconducting means and not during the half-cycles of conduction of saidsecond unidirectionally conducting means.